Respiratory disorders deal with the inability of a sufferer to effect a sufficient exchange of gases with the environment, leading to an imbalance of gases in the sufferer. These disorders can be attributed to a number of different causes. For example, the cause of the disorder may be (1) a pathological consequence of an obstruction of the airway, (2) insufficiency of the lungs in generating negative pressure, (3) an irregularity in the nervous function of the brain stem, or some other disorder. Treatment of such disorders is diverse and depends on the particular respiratory disorder being targeted.
In the first instance, a constriction of the airway, otherwise known as an obstructive apnea or a hypopnea, collectively referred to as obstructive sleep apnea (OSA), can occur when the muscles that normally keep the airway open in a patient relax during slumber to the extent that the airway is constrained or completely closed off, a phenomenon often manifesting itself in the form of snoring. When this occurs for a significant period of time, the patient's brain typically recognizes the threat of hypoxia and partially wakes the patient in order to open the airway so that normal breathing may resume. The patient may be unaware of these occurrences, which may occur as many as several hundred times per session of sleep. This partial awakening may significantly reduce the quality of the patient's sleep, over time potentially leading to a variety of symptoms, including chronic fatigue, elevated heart rate, elevated blood pressure, weight gain, headaches, irritability, depression, and anxiety.
Obstructive sleep apnea is commonly treated with the application of continuous positive airway pressure (CPAP) therapy. Continuous positive airway pressure therapy involves delivering a flow of gas to a patient at a therapeutic pressure above atmospheric pressure that will reduce the frequency and/or duration of apneas and/or hypopneas. This therapy is typically delivered by using a continuous positive airway pressure device (CPAP device) to propel a pressurized stream of air through a conduit to a patient through an interface or mask located on the face of the patient.
Central sleep apnea (CSA) is a type of sleep apnea where the patient stops breathing due to lack of respiratory drive from the brain. CSA is prevalent in approximately 3 to 6% of patients with sleep disorder breathing. However, CSA prevalence drops to about 1.5% after six weeks on CPAP therapy because some patients adapt to the CPAP therapy. Unlike OSA, there is no evidence to-date that CSA can be treated with an increase in positive airway pressure (PAP). On the contrary, some studies suggest that the increase in pressure provided by PAP can trigger additional events called induced CSA. When CSA is detected, it is currently recommended that there be no pressure change responses.